In auto repair shops, for testing high-pressure components of fuel injection systems of motor vehicles, such as high-pressure pumps or fuel injectors, testing units are used which include a fuel accumulator block as a so-called test rail. The higher the test pressures rise in the testing of the high-pressure components, the higher are the temperatures that occur in the test rail. These temperatures are created both by the compression of the test medium (testing oil) of up to 250 MPa and by the friction taking place at the pressure control valves acting as throttles, as well as by heating by the electromagnetic switching valve of the pressure control valve. To cool pressure control valves in common rail installed in motor vehicles, the pressure control valve has fuel flowing around it, which thereby already generates cooling. However, the main quantity of the fuel flows through the fuel injectors. In the case of increased or reduced demand for fuel, its supply is controlled in the supply area of the fuel. Therefore, its flow through the pressure control valve is limited, so that in this instance explicit cooling becomes necessary.
The cooling of a fuel accumulator block (common rail) of a fuel-injection system used in a motor vehicle is described in German Patent Application No. DE 199 45 436 C1. In that document, the fuel accumulator block, besides the main bore acting as pressure accumulator, has lines running parallel to it for cooling the fuel accumulator block, in which a cooling medium is circulating. In addition, it is provided that one should also guide the recirculating leakage from the fuel injector through a leakage line guided through the high-pressure accumulator block, so that the leakage also cools the fuel accumulator block.
Especially in the testing of high-pressure pumps, the entire conveyed quantity flows through the pressure control valves, whereby a considerably higher heat stress arises in the test rail than in a fuel accumulator block (common rail) installed in a motor vehicle. Thus, for example, at pressures of 200 MPa and through-flows of more than 70 liter per hour, the admissible operating temperatures for the pressure control valves are exceeded, whereby in particular, the O-ring seals of the pressure control valves are endangered. Other components, such as pressure sensors or pressure limiting valves, may fail prematurely because of the higher temperatures. Besides, at increasing temperature, the stability of the fuel accumulator block (test rail) becomes decreased, particularly with respect to a high pressure load.